A Predator B unmanned aircraft taxis at the Naval Air Station in Corpus Christi, Texas. / Eric Gay, AP

by Jesse Singal and Naila Inayat, Special for USA TODAY

by Jesse Singal and Naila Inayat, Special for USA TODAY

LAHORE, Pakistan - Human rights groups on Tuesday called on the United States to do more to investigate the numbers of civilians killed and wounded by CIA drone strikes targeting al-Qaeda leaders in Pakistan.

Amnesty International and Human Rights Watch say their researchers have documented cases in which civilians who were not near a terrorist target were killed while laboring in fields or in their homes.

Both reports called for more transparency and accountability in the drone program to ensure it is in compliance with international law.

"As evidence emerges of civilian casualties in these strikes, it's time for the U.S. to stop covering its ears and start taking action to ensure the program is legal," Letta Taylor, a senior counterterrorism researcher at Human Rights Watch, told Al Jazeera.

The extent to which non-combatants have been killed in the drone missile program is not known. The missiles, fired from remote-control-guided planes, are launched on a target based on intelligence that the target is a terrorist. The United States has refused to discuss the secret program overseen by the CIA.

The United States has acknowledged that civilians have been killed in the strikes, but insists that the terrorists themselves are to blame for using family or other civilians as human shields.

Targeting known enemies from the air is not against international law even if there is a chance that civilians may be killed in such strikes. Amnesty said the drone strikes in Pakistan could be war crimes if the USA is not taking proper precautions to prevent civilian casualties when targeting terrorists.

It says the only way to know for sure is for the United States to be more transparent about the program. Human Rights Watch issued similar conclusions about strikes in Yemen.

Many but not all in Pakistan are uneasy about the drone program.

"What makes Human Rights Watch come to this conclusion now when the U.S. government has butchered so many people?" asked Mohammad Ejaz, a 27-year-old mechanical engineer in Lahore.

"When a youngster sees his innocent father dying in such an attack, then he is justified in his hatred."

But Nayyar Afaq, a 32-year-old doctoral student at Quaid-i-Azam University in Islamabad, pointed out that some in Waziristan, the rugged tribal area of Pakistan where U.S. drones operate, support the strikes as a weapon against brutal militants.

"The drones are considered to have the most accurate technology to hit their targets," he said. "Many high-valued commanders of al-Qaeda and the Taliban have been successfully eliminated through the drone strikes."

The U.S. carried out its first drone strike in Pakistan in 2004 under President George W. Bush. President Obama significantly ramped up the attacks when he took office in 2009, the majority of which have been in North Waziristan.

In May, Obama defended the program and revealed that the strikes are authorized only against terrorists who pose a "continuing and imminent threat" to Americans. He said the launch happens only when there is a "near-certainty" that civilians will not be killed or hurt.

He said there was no doubt the program is legal and carried out in a legal manner. Administration officials have told the U.S. media that hundreds of strikes have been launched since their start.

Several organizations have tried to track the number of civilian casualties from nearly 10 years of drone strikes in Pakistan, including the Long War Journal website, the New America Foundation think tank and the Bureau of Investigative journalism.

The groups estimate that the attacks have killed between 2,065 and 3,613 people, and that between 153 and 926 may be civilians.

The Amnesty report said the cases of civilian deaths "raise serious concerns that the USA has unlawfully killed people in drone strikes, and that such killings may amount in some cases to extrajudicial executions or war crimes and other violations of international humanitarian law."

Human Rights Watch urged the Obama administration to "explain the full legal basis on which the U.S. carries out targeted killings," and to "publicly clarify all policy guidelines for targeted killings and disclose when each standard went into effect."

Pakistani Prime Minister Nawaz Sharif is in Washington this week to meet with Obama. Sharif has called to an end for the drone strikes. But the strikes originate from an air base in Pakistan and it is assumed the military and government are aware of the program.

"The problem with trying to understand civilian casualties in the drone debate is severely hindered by the lack of on-the-ground reporting," said Daniel Byman, research director at the Brookings Institution's Saban Center for Middle East Policy.

The Amnesty International report was unusual in that it included accounts from residents of Waziristan. Waziristan "is an area sealed off in part by the Pakistani government," Byman said. "It's rare for reporters and human rights groups and so on to go into these parts."

The claim that some civilians are killed in drone strikes, said Byman, is not controversial. "The controversy comes to how many, and what are the alternatives?"

Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies, has argued that drones often kill terrorists who should instead be captured and interrogated to learn what they know about al-Qaeda operations worldwide. John Woo, a lawyer who counseled the Bush administration on legalities in the war on terror, has warned that drones may be wiping out sources of great intelligence on the terror network.

Either way, Byman said, the human rights reports would probably not have much of an impact on public opinion in the USA.

"I think the overwhelming majority of Americans both favor drones and don't think about them much," he said.